African swine fever virus morphogenesis

Insights and progress on epidemic characteristics, pathogenesis, and preventive measures of African swine fever virus: A review

The African swine fever virus (ASFV) is the only giant double-stranded DNA virus known to be transmitted by insect vectors. It can infect pigs and cause clinical signs such as high fever, bleeding, and splenomegaly, which has been classified as a reportable disease by the WOAH. In 2018, African swine fever (ASF) was introduced into China and rapidly spread to several countries in the Asia-Pacific region, with morbidity and mortality rates reaching 100 percent, resulting in significant economic losses to the global pig industry. Because ASFV has large genomes and a complex escape host mechanism, there are currently no safe and effective drugs or vaccines against it. Therefore, it is necessary to optimize vaccination procedures and find effective treatments by studying the epidemiology of ASFV to reduce economic losses. This article reviews research progress on pathogenesis, genome, proteome and transcriptome, pathogenic mechanisms, and comprehensive control measures of ASFV infection.

Preparation of a new monoclonal antibody against D205R protein of African swine fever virus and identification of its linear antigenic epitope

African swine fever virus (ASFV), a highly contagious virus with a double-stranded DNA genome, is notorious for causing severe hemorrhagic fever in pigs, often leading to mortality rates as high as 100 %. First identified in Kenya in 1921, the virus has since spread globally, with a significant outbreak in China in 2018, causing extensive economic losses in the swine industry. The D205R protein (pD205R) of ASFV, classified as a non-structural protein, plays a role in the transcription of viral genes and is associated with ASFV RNA polymerase. However, the specific function of this protein remains unclear. To gain a deeper insight into the structure, function, and mechanisms of interaction between pD205R and the host, we successfully expressed the pD205R protein and generated a monoclonal antibody (mAb), designated 3G6G1, targeting this protein. The mAb 3G6G1 can be utilized for indirect immunofluorescence (IFA) and Western blotting (WB) detection of ASFV strains. Through the evaluation of the reactivity of antibodies against a series of truncated pD205R fragments, we identified the epitope recognized by mAb 3G6G1 as residing within the amino acid sequence 96 VLSKKNI 102. Bioinformatics analysis indicated that this antigenic epitope possesses a high antigenic index and is highly conserved. These findings will establish a foundation for further research into the function of the D205R protein and its role in the interaction between ASFV and its host.

Virulent African swine fever virus infection of porcine monocytes causes SLA I subversion due to loss of proper ER structure/function

African swine fever virus (ASFV) is a large DNA virus of the Asfarviridae family that causes a fatal hemorrhagic disease in domestic swine and wild boar. Infections with moderately virulent strains predominantly result in a milder clinical course and lower lethality. As target cells of ASFV, monocytes play a crucial role in triggering T-cell-mediated immune defense and ASF pathogenesis. We compared the effect of the highly virulent "Armenia2008" (ASFV-A) virus strain with that of the naturally attenuated "Estonia2014" (ASFV-E) on cellular immune activation in vivo and on primary monocytes ex vivo. Specifically, we asked whether antigen presentation of porcine monocytes is impaired upon ASFV-A infection. ASFV-A-infected monocytes are characterized by lower levels of swine leukocyte antigen (SLA) class I on the cell surface than ASFV-E-infected and uninfected monocytes. Despite stable steady-state SLA I mRNA/protein levels and expression of critical components of the antigen processing machinery, a marked decrease in maturation and reduced surface transport of SLA I were observed in ASFV-A-infected monocytes. The intracellular maturation block of SLA I was accompanied by a loss of functional rough ER structures and a pronounced formation of ER-associated aggresomes. This unsolved cellular stress resulted in a shutdown of overall host cell protein translation, mitochondrial dysfunction, and caspase-3-mediated apoptosis. In contrast, no such cellular subversion phenomenon was found in ASFV-E-infected monocytes. Our findings suggest that in domestic pigs infected with highly virulent ASFV-A, sequential subversion events occur in infected monocytes, likely leading to compromised T-cell activation and impaired downstream responses against ASFV.

Transcriptome Profiling Reveals That the African Swine Fever Virus C315R Exploits the IL-6 STAT3 Signaling Axis to Facilitate Virus Replication

African swine fever (ASF) is an acute and highly contagious disease that has caused great losses in the past years. It is caused by African swine fever virus (ASFV), which is a large DNA virus encoding about 165 genes. It has been shown that the purified extracellular ASFV is internalized by both constitutive macropinocytosis and clathrin-mediated endocytosis, and the virus utilizes apoptotic bodies for infection and cell cell transmission. The ASFV-encoded RNA polymerase subunit C315R is thought to play an important role in ASFV replication and transcription. However, its involvement in ASFV infection, particularly in host response, remains only partially understood. In this study, the role of C315R in enhancing ASFV replication was investigated through RNA-Seq transcriptomic analysis, which was based on 3D4/21 cells transfected the plasmid expressing HA-tagged C315R or the empty vector. Our findings revealed that C315R significantly upregulates the expression of inflammatory mediators with a particular emphasis on IL-6. The most differentially expressed genes (DEGs) were predominantly associated with the TNF, IL-17, MAPK, and JAK STAT signaling pathways. RNA-seq results were validated through RT-PCR. Subsequently, we observed that ASFV infection increases IL-6 expression and STAT3 phosphorylation, which is regulated by the ASFV C315R protein. Notably, inhibiting STAT3 phosphorylation with specific inhibitors suppressed ASFV replication. In conclusion, our study demonstrates that the ASFV C315R protein actives STAT3 phosphorylation through promoting the transcription of IL-6 to facilitate virus replication. These findings highlight C315R as a positive regulator in the IL-6 STAT3 signaling axis during ASFV infection.

The Deletion of the MGF360-10L/505-7R Genes of African Swine Fever Virus Results in High Attenuation but No Protection Against Homologous Challenge in Pigs

African swine fever virus (ASFV) is the causative agent of African swine fever (ASF), a severe hemorrhagic disease with a mortality rate reaching 100%. Despite extensive research on ASFV mechanisms, no safe and effective vaccines or antiviral treatments have been developed. Live attenuated vaccines generated via gene deletion are considered to be highly promising. We developed a novel recombinant ASFV strain by deleting MGF360-10L and MGF505-7R, significantly reducing virulence in pigs. In the inoculation experiment, pigs were infected with 104 50% hemadsorption doses (HAD50) of the mutant strain. All the animals survived the observation period without showing ASF-related clinical signs. Importantly, no significant viral infections were detected in the cohabitating pigs. In the virus challenge experiment, all pigs succumbed after being challenged with the parent strain. RNA-seq analysis showed that the recombinant virus induced slightly higher expression of natural immune factors than the parent ASFV; however, this level was insufficient to provide immune protection. In conclusion, our study demonstrates that deleting MGF360-10L and MGF505-7R from ASFV CN/GS/2018 significantly reduces virulence but fails to provide protection against the parent strain.

From structure prediction to function: defining the domain on the African swine fever virus CD2v protein required for binding to erythrocytes

African swine fever virus (ASFV) is a high-consequence pathogen posing a substantial threat to global food security. This large DNA virus encodes more than 150 open reading frames, many of which are uncharacterized. The EP402R gene encodes CD2v, a glycoprotein expressed on the surface of infected cells and the only viral protein known to be present in the virus external envelope. This protein mediates binding of erythrocytes to both cells and virions. This interaction is known to prolong virus persistence in blood thus facilitating viral transmission. The sequence of the extracellular domain of CD2v shows similarity with that of mammalian CD2 proteins and is therefore likely to feature two immunoglobulin (Ig)-like domains. A combination of protein structure modeling and extensive mutagenesis was used to identify residues mediating binding of transiently expressed CD2v to erythrocytes. The N-terminal Ig-like domain AGFCC'C″ β sheet was identified as the putative CD2v erythrocyte-binding area. This region differed from the putative CD58 ligand binding site of host CD2, suggesting that CD2v may bind to a ligand(s) other than CD58. An attenuated genotype I ASFV was constructed by replacing the wild-type EP402R gene for a mutant form expressing CD2v bearing a single amino acid substitution, which abrogated the binding to erythrocytes. Pigs immunized with the recombinant virus developed early antibody and cellular responses, low levels of viremia, mild clinical signs post-immunization, and high levels of protection against challenge. These findings improve our understanding of virus-host interactions and provide a promising approach to modified live vaccine development.

IMPORTANCE

A better understanding of the interactions between viruses and their hosts is a crucial step in the development of strategies for controlling viral diseases, such as vaccines and antivirals. African swine fever, a pig disease with fatality rates approaching 100%, causes very substantial economic losses in affected countries, and new control measures are clearly needed. In this study, we characterized the interaction between the ASFV CD2v protein and host erythrocytes. The interaction plays a key role in viral persistence in blood since it can allow the virus to "hide" from the host immune system. We identified the amino acids in the viral protein that mediate the interaction with erythrocytes and used this information to construct a mutant virus that is no longer able to bind these cells. This virus induces strong immune responses that provide high levels of protection against infection with the deadly parental virus.

Cell entry mechanisms of African swine fever virus

African swine fever virus (ASFV) is a highly complex virus that poses a significant threat to the global swine industry. However, little is known about the mechanisms of ASFV cell entry because ASFV has a multilayered structure and a genome encoding over 150 proteins. This review aims to elucidate the current knowledge on cell entry mechanisms of ASFV and the cellular and viral proteins involved. Experimental evidence suggests that ASFV utilises multiple pathways for entry, which may be cell or tissue type dependent, but the intricate nature of ASFV has hindered the identification of cellular and viral proteins involved in this process. Therefore, further research into the molecular virology of ASFV is essential to advance our understanding of the ASFV entry mechanisms, which will pave the way for innovative strategies to combat this formidable pathogen.

Pathogenicity and virulence of African swine fever virus

African swine fever (ASF) is a devastating disease with a high impact on the pork industry worldwide. ASF virus (ASFV) is a very complex pathogen, the sole member of the family Asfaviridae, which induces a state of immune suppression in the host through infection of myeloid cells and apoptosis of lymphocytes. Moreover, haemorrhages are the other main pathogenic effect of ASFV infection in pigs, related to the infection of endothelial cells, as well as the activation and structural changes of this cell population by proinflammatory cytokine upregulation within bystander monocytes and macrophages. There are still many gaps in the knowledge of the role of proteins produced by the ASFV, which is related to the difficulty in producing a safe and effective vaccine to combat the disease, although few candidates have been approved for use in Southeast Asia in the past couple of years.

Ultra-rapid and sensitive detection of African swine fever virus using multiple cross displacement amplification combined with nanoparticle-based lateral flow biosensor

African swine fever (ASF) is a devastating disease that can kill almost all infected pigs, causing great damage to the pig industry and destabilizing the global economy. Here, we developed a specific assay that combined multiple cross-displacement amplification (MCDA) with a nanoparticle-based lateral flow biosensor (LFB) for early and rapid identification of the African swine fever virus (ASFV-MCDA-LFB). We first designed a set of MCDA primers to recognize 10 different regions of the target ASFV B646L gene. Subsequently, the MCDA reaction was monitored with various methods: MG chromogenic reagents, agarose gel electrophoresis, real-time turbidity, and LFB. The ASFV-MCDA-LFB assay was optimized and evaluated with target nucleic acid templates extracted from various pathogens and simulated whole blood samples. As a result, the detection of limit (LOD) of the ASFV assay was 200 copies/reaction within 30 min, and no cross-reaction were observed with other non-ASFV viruses and common pathogens in this study. The evaluation assays demonstrated that the ASFV-MCDA-LFB method here is rapid, objective, easy-to-use, and low-cost detection method which can be used as a diagnostic or screening tool with competitive potential for point-of-care testing (POCT) of ASFV.

Transcription regulation of African swine fever virus: dual role of M1249L

African swine fever virus (ASFV), which poses significant risks to the global economy, encodes a unique host-independent transcription system. This system comprises an eight-subunit RNA polymerase (vRNAP), temporally expressed transcription factors and transcript associated proteins, facilitating cross-species transmission via intermediate host. The protein composition of the virion and the presence of transcription factors in virus genome suggest existence of distinct transcription systems during viral infection. However, the precise mechanisms of transcription regulation remain elusive. Through analyses of dynamic transcriptome, vRNAP-associated components and cell-based assay, the critical role of M1249L in viral transcription regulation has been highlighted. Atomic-resolution structures of vRNAP-M1249L supercomplex, exhibiting a variety of conformations, have uncovered the dual functions of M1249L. During early transcription, M1249L could serve as multiple temporary transcription factors with C-terminal domain acting as a switcher for activation/inactivation, while during late transcription it aids in the packaging of the transcription machinery. The structural and functional characteristics of M1249L underscore its vital roles in ASFV transcription, packaging, and capsid assembly, presenting novel opportunities for therapeutic intervention.

TRIM28 regulates the coagulation cascade inhibited by p72 of African swine fever virus

In 2018, African swine fever virus (ASFV) emerged in China, causing extremely serious economic losses to the domestic pig industry. Infection with ASFV can cause disseminated coagulation, leading to the consumption of platelets and coagulation factors and severe bleeding. However, the mechanism of virus-induced coagulation has yet to be established. In our study, ASFV downregulated the coagulation process, as detected by D-dimer (D2D) and Factor X (F10) expression in pigs challenged with ASFV HLJ/18. In vitro, ASFV infection increased Factor IX (F9) and Factor XII (F12) expression while downregulating F10 expression in porcine alveolar macrophages (PAMs). African swine fever virus induced both intrinsic and extrinsic coagulation cascades. In addition, several encoded proteins affect the expression of the crucial coagulation protein F10, and among the encoded proteins, p72 inhibits the activity and expression of F10. Proteomic analysis also revealed that p72 is involved in the coagulation cascade. p72 can interact with F10, and its inhibitory functional domains include amino acids 423-432 and amino acids 443-452. Finally, we found that F10 and p72 interact with tripartite motif-containing protein 28 (TRIM28). TRIM28 knockdown resulted in a decrease in F10 expression. Importantly, TRIM28 contributes to the reduction in F10 protein expression regulated by p72. Our findings revealed an inhibitory effect of the viral protein p72 on the ASFV infection-induced coagulation cascade and revealed a role of TRIM28 in reducing F10 expression, revealing a molecular mechanism of ASFV-associated coagulation.

Identification of a novel conserved B-cell epitope in p15 of the African swine fever virus

African Swine Fever Virus (ASFV), a highly contagious DNA virus, causes severe economic losses to the global swine industry. The ASFV p15 protein, which is found in the core shell, is essential to the assembly of viral particles. In addition, protein p15 is a candidate target for the development of diagnostic reagents for African Swine Fever (ASF) because of its excellent immunogenicity. In this research, we prepared the p15 protein using eukaryotic expression system and validated it with sera from ASFV-infected pigs. The p15 protein could be well identified by the sera from ASFV-infected pigs, suggesting that some linear epitopes are located in the p15 protein. Furthermore, we successfully prepared two lgG1 subclass monoclonal antibodies (1E6-A7 and 3D6-D4) specific against p15 using hybridoma technology. Using the peptide scanning method, we discovered the two mAbs well recognized the same linear epitope23LEIINNLCML32. The23LEIINNLCML32 epitope in the ASFV p15 N-terminus was identified and characterized for the first time, and it reacted well with the ASFV-positive serum, implying that it was a natural B cell linear epitope. These findings may help in the development of novel serologic diagnosis tools and the improvement of antiviral drug designs for ASF.

Assessment of Nine Real-Time PCR Kits for African Swine Fever Virus Approved in Republic of Korea

The African swine fever virus (ASFV) causes severe disease in wild and domestic pigs, with high mortality rates, extensive spread, and significant economic losses globally. Despite ongoing efforts, an effective vaccine remains elusive. Therefore, effective diagnostic methods are needed to rapidly detect and prevent the further spread of ASF. This study assessed nine commercial kits based on real-time polymerase chain reaction (PCR) approved in the Republic of Korea using the synthesized ASFV plasmid, 20 food waste samples, and artificially spiked samples (ASSs). The kits were evaluated for their diagnostic sensitivity, specificity, cost per reaction, and reaction running time. In addition, the results were compared with those of the World Organization for Animal Health (WOAH) standard methods. Three commercial kits (VDx® ASFV qPCR Kit, Palm PCR™ ASFV Fast PCR Kit, and PowerChek™ ASFV Real-time PCR Detection Kit Ver.1.0) demonstrated the highest sensitivity (100 ag/μL), cost-effectiveness (less than KRW 10,000), and shortest running time (less than 70 min). These kits are suitable for the monitoring, early diagnosis, and prevention of the spread of ASF. This is the first report on the performance comparison of ASFV diagnostic kits approved in the Republic of Korea, providing valuable information for selecting kits for testing with food waste samples.

Strategic nucleic acid detection approaches for diagnosing African swine fever (ASF): navigating disease dynamics

African swine fever (ASF) is a devastating disease caused by African swine fever virus (ASFV) and leads to significant economic losses in the pig farming industry. Given the absence of an effective vaccine or treatment, the mortality rate of ASF is alarmingly close to 100%. Consequently, the ability to rapidly and accurately detect ASFV on site and promptly identify infected pigs is critical for controlling the spread of this pandemic. The dynamics of the ASF virus load and antibody response necessitate the adoption of various detection strategies at different stages of infection, a topic that has received limited attention to date. This review offers detailed guidance for choosing appropriate ASF diagnostic techniques tailored to the clinical manifestations observed from the acute to chronic phases, including asymptomatic cases. We comprehensively summarize and evaluate the latest advancements in ASFV detection methods, such as CRISPR-based diagnostics, biosensors, and microfluidics. Additionally, we address the challenges of false negatives or positives due to ASF variants or the use of injected live attenuated vaccines. This review provides an exhaustive list of diagnostic tests suitable for detecting each stage of symptoms and potential target genes for developing new detection methods. In conclusion, we highlight the current challenges and future directions in ASFV detection, underscoring the need for continued research and innovation in this field.

Navigating the threat of African swine fever: a comprehensive review

African swine fever (ASF) is caused by Asfivirus and has become one of the most important diseases of swine in recent years. ASF was an endemic disease of the sub-Saharan Africa but later spread to various parts of the world. The infection in ticks and wild swine, alongside global pork trade, drives its spread and persistence. Once introduced to an area, the disease is difficult to eliminate due to sylvatic, domestic, and tick-swine transmission cycles. Because of the existence of various modes of transmission of the ASF virus, biosecurity measures have not been very successful. The line of treatment is not of much use and the outcome of this disease is usually fatal. The prognosis or the recovery of the animal depends on the virulence of the strain involved. Development of vaccines has been attempted but to date has not been very successful. This review focuses on the basic context of ASF, the challenges associated with it, and the options that might be available to prevent its occurrence which includes the different vaccine development strategies tried and tested till now.

African swine fever; insights into genomic aspects, reservoirs and transmission patterns of virus

African swine fever is a hemorrhagic disease of pigs with high mortality rates. Since its first characterization in 1921, there has been sufficient information about African swine fever virus (ASFV) and related diseases. The virus has been found and maintained in the sylvatic cycle involving ticks and domestic and wild boars in affected regions. The ASFV is spread through direct and indirect contact with infected pigs, their products and carrier vectors especially Ornithodoros ticks. Severe economic losses and a decline in pig production have been observed in ASFV affected countries, particularly in sub-Saharan Africa and Europe. At the end of 2018, the ASFV adversely affected China, the world's leading pork-producer. Control strategies for the disease remained challenging due to the unavailability of effective vaccines and the lack of successful therapeutic measures. However, considerable efforts have been made in recent years to understand the biology of the virus, surveillance and effective control measures. This review emphasizes and summarizes the current state of information regarding the knowledge of etiology, epidemiology, transmission, and vaccine-based control measures against ASFV.

Identification of two novel linear epitopes on the E165R protein of African swine fever virus recognized by monoclonal antibodies

African swine fever (ASF) is a highly fatal infectious disease in pigs, caused by the African swine fever virus (ASFV). It is characterized by short disease duration and high morbidity and mortality. In August 2018, ASF was first reported in China and it subsequently spread rapidly throughout the country, causing serious economic losses for the Chinese pig industry. Early detection plays a critical role in preventing and controlling ASF because there is currently no effective vaccine or targeted therapeutic medication available. Additionally, identifying conserved protective antigenic epitopes of ASFV is essential for the development of diagnostic reagents. The E165R protein, which is highly expressed in the early stages of ASFV infection, can serve as an important indicator for early detection. In this study, we successfully obtained high purity soluble prokaryotic expression of the E165R protein. We then utilized the purified recombinant E165R protein for immunization in mice to prepare monoclonal antibodies (mAbs) using the hybridoma fusion technique. After three subclonal screens, we successfully obtained three mAbs against ASFV E165R protein in cells named 1B7, 1B8, and 10B8. Through immunofluorescence assay (IFA) and Western blot, we confirmed that the prepared mAbs specifically recognize the baculovirus-expressed E165R protein. By using overlapping truncated E165R protein and overlapping peptide scanning analysis, we tentatively identified two novel linear B cell epitopes (13EAEAYYPPSV22 and 55VACEHMGKKC64) that are highly conserved in genotype I and genotype II of ASFV. Thus, as a detection antibody, it has the capability to detect ASFV across a wide range of genotypes, providing valuable information for the development of related immunodiagnostic reagents.

Development of plate-type and tubular chemiluminescence immunoassay against African swine fever virus p72

African swine fever (ASF) is a highly contagious and fatal viral disease that has caused huge economic losses to the pig and related industries worldwide. At present, rapid, accurate, and sensitive laboratory detection technologies are important means of preventing and controlling ASF. However, because attenuated strains of African swine fever virus (ASFV) are constantly emerging, an ASFV antibody could be used more effectively to investigate the virus and control the disease on pig farms. The isolation of ASFV-specific antibodies is also essential for the diagnosis of ASF. Therefore, in this study, we developed two chemiluminescence immunoassays (CLIAs) to detect antibodies directed against ASFV p72: a traditional plate-type blocking CLIA (p72-CLIA) and an automatic tubular competitive CLIA based on magnetic particles (p72-MPCLIA). We compared the diagnostic performance of these two methods to provide a feasible new method for the effective prevention and control of ASF and the purification of ASFV. The cut-off value, diagnostic sensitivity (Dsn), and diagnostic specificity (Dsp) of p72-CLIA were 40%, 100%, and 99.6%, respectively, in known background serum, whereas those of p72-MPCLIA were 36%, 100%, and 99.6%, respectively. Thus, both methods show good Dsn, Dsp, and repeatability. However, when analytical sensitivity was evaluated, p72-MPCLIA was more sensitive than p72-CLIA or a commercial enzyme-linked immunosorbent assay. More importantly, p72-MPCLIA reduced the detection time to 15 min and allowed fully automated detection. In summary, p72-MPCLIA showed superior diagnostic performance and offered a new tool for detecting ASFV infections in the future. KEY POINTS: • Two chemiluminescence immunoassay (plate-type CLIA and tubular CLIA) methods based on p72 monoclonal antibody (mAb) were developed to detect ASFV antibody. • Both methods show good diagnostic performance (Dsn (100%), Dsp (99.6%), and good repeatability), and p72-MPCLIA detects antibodies against ASFV p72 with high efficiency in just 15 min.

African Swine Fever Virus Immunosuppression and Virulence-Related Gene

African swine fever virus (ASFV), a highly contagious pathogen characterized by a complex structure and a variety of immunosuppression proteins, causes hemorrhagic, acute, and aggressive infectious disease that severely injures the pork products and industry. However, there is no effective vaccine or treatment. The main reasons are not only the complex mechanisms that lead to immunosuppression but also the unknown functions of various proteins. This review summarizes the interaction between ASFV and the host immune system, along with the involvement of virulence-related genes and proteins, as well as the corresponding molecular mechanism of immunosuppression of ASFV, encompassing pathways such as cGAS-STING, nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), Janus Kinase (JAK) and JAK Signal Transducers and Activators of Transcription (STAT), apoptosis, and other modulation. The aim is to summarize the dynamic process during ASFV infection and entry into the host cell, provide a rational insight into development of a vaccine, and provide a better clear knowledge of how ASFV impacts the host.

Comprehensive Characterization of the Genetic Landscape of African Swine Fever Virus: Insights into Infection Dynamics, Immunomodulation, Virulence and Genes with Unknown Function

African Swine Fever (ASF) is a lethal contagious hemorrhagic viral disease affecting the swine population. The causative agent is African Swine Fever Virus (ASFV). There is no treatment or commercial vaccine available at present. This virus poses a significant threat to the global swine industry and economy, with 100% mortality rate in acute cases. ASFV transmission occurs through both direct and indirect contact, with control measures limited to early detection, isolation, and culling of infected pigs. ASFV exhibits a complex genomic structure and encodes for more than 50 structural and 100 non-structural proteins and has 150 to 167 open reading frames (ORFs). While many of the proteins are non-essential for viral replication, they play crucial roles in mediating with the host to ensure longevity and transmission of virus in the host. The dynamic nature of ASFV research necessitates constant updates, with ongoing exploration of various genes and their functions, vaccine development, and other ASF-related domains. This comprehensive review aims to elucidate the structural and functional roles of both newly discovered and previously recorded genes involved in distinct stages of ASFV infection and immunomodulation. Additionally, the review discusses the virulence genes and genes with unknown functions, and proposes future interventions.

Identification of Two Linear Epitopes on MGF_110-13L Protein of African Swine Fever Virus with Monoclonal Antibodies

African swine fever caused by African swine fever virus (ASFV) is an acute, highly contagious swine disease with high mortality. To facilitate effective vaccine development and find more serodiagnostic targets, fully exploring the ASFV antigenic proteins is urgently needed. In this study, the MGF_110-13L was identified as an immunodominant antigen among the seven transmembrane proteins. The main outer-membrane domain of MGF_110-13L was expressed and purified. Two monoclonal antibodies (mAbs; 8C3, and 10E4) against MGF_110-13L were generated. The epitopes of two mAbs were preliminary mapped with the peptide fusion proteins after probing with mAbs by enzyme-linked immunosorbent assay (ELISA) and Western blot. And the two target epitopes were fine-mapped using further truncated peptide fusion protein strategy. Finally, the core sequences of mAbs 8C3 and 10E4 were identified as 48WDCQDGICKNKITESRFIDS67, and 122GDHQQLSIKQ131, respectively. The peptides of epitopes were synthesized and probed with ASFV antibody positive pig sera by a dot blot assay, and the results showed that epitope 10E4 was an antigenic epitope. The epitope 10E4 peptide was further evaluated as a potential antigen for detecting ASFV antibodies. To our knowledge, this is the first report of antigenic epitope information on the antigenic MGF_110-13L protein of ASFV.

The Distal Promoter of the B438L Gene of African Swine Fever Virus Is Responsible for the Transcription of the Alternatively Spliced B169L

The B169L protein (pB169L) of African swine fever virus (ASFV) is a structural protein with an unidentified function during the virus replication. The sequences of the B169L gene and the downstream B438L gene are separated by short intergenic regions. However, the regulatory mode of the gene transcription remains unknown. Here, we identified two distinct promoter regions and two transcription start sites (TSSs) located upstream of the open reading frame (ORF) of B438L. Using the promoter reporter system, we demonstrated that the cis activity of the ORF proximal promoter exhibited significantly higher levels compared with that of the distal promoter located in the B169L gene. Furthermore, transfection with the plasmids with two different promoters for B438L could initiate the transcription and expression of the B438L gene in HEK293T cells, and the cis activity of the ORF proximal promoter also displayed higher activities compared with the distal promoter. Interestingly, the B438L distal promoter also initiated the transcription of the alternatively spliced B169L mRNA (B169L mRNA2) encoding a truncated pB169L (tpB169L) (amino acids 92-169), and the gene transcription efficiency was increased upon mutation of the initiation codon located upstream of the alternatively spliced B169L gene. Taken together, we demonstrated that the distal promoter of B438L gene initiates the transcription of both the B438L mRNA and B169L mRNA2. Comprehensive analysis of the transcriptional regulatory mode of the B438L gene is beneficial for the understanding of the association of B438L protein and pB169L and the construction of the gene-deleted ASFV.

Function investigation of p11.5 in ASFV infection

Virus replication relies on complex interactions between viral proteins. In the case of African swine fever virus (ASFV), only a few such interactions have been identified so far. In this study, we demonstrate that ASFV protein p72 interacts with p11.5 using co-immunoprecipitation and liquid chromatography-mass spectrometry (LC-MS). It was found that protein p72 interacts specifically with p11.5 ​at sites amino acids (aa) 1-216 of p72 and aa 1-68 of p11.5. To assess the importance of p11.5 in ASFV infection, we developed a recombinant virus (ASFVGZΔA137R) by deleting the A137R gene from the ASFVGZ genome. Compared with ASFVGZ, the infectious progeny virus titers of ASFVGZΔA137R were reduced by approximately 1.0 logs. In addition, we demonstrated that the growth defect was partially attributable to a higher genome copies-to-infectious virus titer ratios produced in ASFVGZΔA137R-infected MA104 ​cells than in those infected with ASFVGZ. This finding suggests that MA104 ​cells infected with ASFVGZΔA137R may generate larger quantities of noninfectious particles. Importantly, we found that p11.5 did not affect virus-cell binding or endocytosis. Collectively, we show for the first time the interaction between ASFV p72 and p11.5. Our results effectively provide the relevant information of the p11.5 protein. These results extend our understanding of complex interactions between viral proteins, paving the way for further studies of the potential mechanisms and pathogenesis of ASFV infection.

Evaluation of early African swine fever virus detection using CP204L gene encoding the p30 protein using quantitative polymerase chain reaction

Background and Aim

The African swine fever virus (ASFV), spanning 170-193 kb, contains over 200 proteins, including p72 and p30, which play crucial roles in the virus's entry and expression. This study investigated the capability of detecting ASFV early through the analysis of genes B646L and CP204L, encoding p72 and p30 antigen proteins, by employing ASFV, diagnosis, immunohistochemistry (IHC), quantitative polymerase chain reaction (qPCR), and IHC techniques.

Materials and Methods

Samples were taken from both experimentally and field-infected pigs to evaluate the effectiveness of qPCR and IHC in detecting ASFV. Twenty-two infected pigs were necropsied at 3-, 5-, 7-, and 9-day post-infection to obtain the first set of samples, collecting anticoagulated blood and tissues each time. The thymus, spleen, and lymph nodes were processed by fixing in 10% formalin, paraffin-blocking, and undergoing IHC staining. Forty anticoagulated blood samples were collected from clinically infected sows at a pig farm for the second batch of samples. Based on the lowest Ct values, three blood samples were diluted fivefold for qPCR DNA testing, and their tissues were used for both qPCR and IHC analyses.

Results

At 1-day post-infection, p30-qPCR identified more ASFV-positive pigs and measured lower Ct values compared to p72-qPCR. At later time points, both methods showed similar levels of detection. ASFV was detected earlier and with lower Ct values in lymphoid tissues using p30-qPCR compared to p72-qPCR, particularly in the spleen and lymph nodes. In a field outbreak study, p30-qPCR demonstrated superior sensitivity and lower Ct values when detecting ASFV in blood samples compared to p72-qPCR.

Conclusion

The early detection of the CP204L gene encoding p30 and its corresponding antigenic protein in ASFV diagnosis compared to the gene encoding p72 suggests that CP204L and p30 are promising candidates for the development of more effective antigen and antibody testing methods.

Development of novel monoclonal antibodies for blocking NF-κB activation induced by CD2v protein in African swine fever virus

Background

CD2v, a critical outer envelope glycoprotein of the African swine fever virus (ASFV), plays a central role in the hemadsorption phenomenon during ASFV infection and is recognized as an essential immunoprotective protein. Monoclonal antibodies (mAbs) targeting CD2v have demonstrated promise in both diagnosing and combating African swine fever (ASF). The objective of this study was to develop specific monoclonal antibodies against CD2v.

Methods

In this investigation, Recombinant CD2v was expressed in eukaryotic cells, and murine mAbs were generated through meticulous screening and hybridoma cloning. Various techniques, including indirect enzyme-linked immunosorbent assay (ELISA), western blotting, immunofluorescence assay (IFA), and bio-layer interferometry (BLI), were employed to characterize the mAbs. Epitope mapping was conducted using truncation mutants and epitope peptide mapping.

Results

An optimal antibody pair for a highly sensitive sandwich ELISA was identified, and the antigenic structures recognized by the mAbs were elucidated. Two linear epitopes highly conserved in ASFV genotype II strains, particularly in Chinese endemic strains, were identified, along with a unique glycosylated epitope. Three mAbs, 2B25, 3G25, and 8G1, effectively blocked CD2v-induced NF-κB activation.

Conclusions

This study provides valuable insights into the antigenic structure of ASFV CD2v. The mAbs obtained in this study hold great potential for use in the development of ASF diagnostic strategies, and the identified epitopes may contribute to vaccine development against ASFV.

Overview of Modern Commercial Kits for Laboratory Diagnosis of African Swine Fever and Swine Influenza A Viruses

Rapid and early detection of infectious diseases in pigs is important, especially for the implementation of control measures in suspected cases of African swine fever (ASF), as an effective and safe vaccine is not yet available in most of the affected countries. Additionally, analysis for swine influenza is of significance due to its high morbidity rate (up to 100%) despite a lower mortality rate compared to ASF. The wide distribution of swine influenza A virus (SwIAV) across various countries, the emergence of constantly new recombinant strains, and the danger of human infection underscore the need for rapid and accurate diagnosis. Several diagnostic approaches and commercial methods should be applied depending on the scenario, type of sample and the objective of the studies being implemented. At the early diagnosis of an outbreak, virus genome detection using a variety of PCR assays proves to be the most sensitive and specific technique. As the disease evolves, serology gains diagnostic value, as specific antibodies appear later in the course of the disease (after 7-10 days post-infection (DPI) for ASF and between 10-21 DPI for SwIAV). The ongoing development of commercial kits with enhanced sensitivity and specificity is evident. This review aims to analyse recent advances and current commercial kits utilised for the diagnosis of ASF and SwIAV.

Characterization of the monoclonal antibody and the immunodominant B-cell epitope of African swine fever virus pA104R by using mouse model

The African swine fever virus (ASFV) structural protein pA104R is the only histone-like protein encoded by eukaryotic viruses. pA104R is an essential DNA-binding protein required for DNA replication and genome packaging of ASFV, which are vital for pathogen survival and proliferation. pA104R is an important target molecule for diagnosing, treating, and immune prevention of ASFV. This study characterized monoclonal antibodies (mAbs) against pA104R and found them to recognize natural pA104R in ASFV strains with different genotypes, showing high conservation. Confirmation analyses of pA104R epitopes using mAbs indicated the presence of immunodominant B-cell epitopes, and further characterization showed the high antigenic index and surface accessibility coefficients of the identified epitope. Furthermore, the pA104R protein functions through the polar interactions between the binding amino acid sites; however, these interactions may be blocked by the recognition of generated mAbs. Characterizing the immunodominant B-cell epitope of the ASFV critical proteins, such as pA104R, may contribute to developing sensitive diagnostic tools and vaccine candidate targets.IMPORTANCEAfrican swine fever (ASF) is a highly pathogenic, lethal, and contagious viral disease affecting domestic pigs and wild boars. As no effective vaccine or other treatments have been developed, the control of African swine fever virus (ASFV) relies heavily on virus detection and diagnosis. A potential serological target is the structural protein pA104R. However, the molecular basis of pA104R antigenicity remains unclear, and a specific monoclonal antibody (mAb) against this protein is still unavailable. In this study, mAbs against pA104R were characterized and found to recognize natural pA104R in ASFV strains with different genotypes. In addition, confirmation analyses of pA104R epitopes using mAbs indicated the presence of immunodominant B-cell epitopes, and further characterization showed the high antigenic index and surface accessibility coefficients of the identified epitope. Characteristics of the immunodominant B-cell epitope of ASFV proteins, such as pA104R, may contribute to developing sensitive diagnostic tools and identifying vaccine candidate targets.

Identification of a novel linear B-cell epitope on the p30 protein of African swine fever virus using monoclonal antibodies

The outbreak of African Swine Fever (ASF) has caused huge economic losses to the pig industry. There are no safe and effective vaccines or diagnostics available. The p30 protein serves as a key target for the detection of ASFV antibodies and is an essential antigenic protein for early serological diagnosis. Here, the p30 protein was purified after being expressed in E. coli and its immunogenicity was verified in sera from pigs naturally infected with ASFV. Furthermore, a monoclonal antibody (McAb) designated as McAb 1B4G2-4 (subtype IgG1/kappa-type) was produced and it was verified to specifically recognize the ASFV Pig/HLJ/2018/strain and eukaryotic recombinant ASFV p30 protein. The epitope identified by McAb 1B4G2-4, defining the unique B-cell epitope 164HNFIQTI170, was located using peptide scanning. Comparing amino acid (aa) sequence revealed that this epitope is conserved in all reference ASFV strains from different regions of China, including the highly pathogenic strain Georgia 2007/1 (NC_044959.2) that is widely distributed. It is also exposed to the surface of the p30 protein, suggesting that it could be an important B-cell epitope. Our study may serve as a basis for the development of serological diagnostic methods and subunit vaccines.

Recent progress and major gaps in the vaccine development for African swine fever

The swine industry across the globe is recently facing a devastating situation imparted by a highly contagious and deadly viral disease, African swine fever. The disease is caused by a DNA virus, the African swine fever virus (ASFV) of the genus Asfivirus. ASFV affects both wild boars and domestic pigs resulting in an acute form of hemorrhagic fever. Since the first report in 1921, the disease remains endemic in some of the African countries. However, the recent occurrence of ASF outbreaks in Asia led to a fresh and formidable challenge to the global swine production industry. Culling of the infected animals along with the implementation of strict sanitary measures remains the only options to control this devastating disease. Efforts to develop an effective and safe vaccine against ASF began as early as in the mid-1960s. Different approaches have been employed for the development of effective ASF vaccines including inactivated vaccines, subunit vaccines, DNA vaccines, virus-vectored vaccines, and live attenuated vaccines (LAVs). Inactivated vaccines are a non-feasible strategy against ASF due to their inability to generate a complete cellular immune response. However genetically engineered vaccines, such as subunit vaccines, DNA vaccines, and virus vector vaccines, represent tailored approaches with minimal adverse effects and enhanced safety profiles. As per the available data, gene deleted LAVs appear to be the most potential vaccine candidates. Currently, a gene deleted LAV (ASFV-G-∆I177L), developed in Vietnam, stands as the sole commercially available vaccine against ASF. The major barrier to the goal of developing an effective vaccine is the critical gaps in the knowledge of ASFV biology and the immune response induced by ASFV infection. The precise contribution of various hosts, vectors, and environmental factors in the virus transmission must also be investigated in depth to unravel the disease epidemiology. In this review, we mainly focus on the recent progress in vaccine development against ASF and the major gaps associated with it.

Deleting the C84L Gene from the Virulent African Swine Fever Virus SY18 Does Not Affect Its Replication in Porcine Primary Macrophages but Reduces Its Virulence in Swine

(1) Background: African swine fever (ASF) is a highly contagious disease that causes high pig mortality. Due to the absence of vaccines, prevention and control are relatively challenging. The pathogenic African swine fever virus (ASFV) has a complex structure and encodes over 160 proteins, many of which still need to be studied and verified for their functions. In this study, we identified one of the unknown functional genes, C84L. (2) Methods: A gene deficient strain was obtained through homologous recombination and several rounds of purification, and its replication characteristics and virulence were studied through in vitro and in vivo experiments, respectively. (3) Results: Deleting this gene from the wild-type virulent strain SY18 did not affect its replication in porcine primary macrophages but reduced its virulence in pigs. In animal experiments, we injected pigs with a 102 TCID50, 105 TCID50 deletion virus, and a 102 TCID50 wild-type strain SY18 intramuscularly. The control group pigs reached the humane endpoint on the ninth day (0/5) and were euthanized. Two pigs in the 102 TCID50(2/5) deletion virus group survived on the twenty-first day, and one in the 105 TCID50(1/5) deletion virus group survived. On the twenty-first day, the surviving pigs were euthanized, which was the end of the experiment. The necropsies of the survival group and control groups' necropsies showed that the surviving pigs' liver, spleen, lungs, kidneys, and submaxillary lymph nodes did not show significant lesions associated with the ASFV. ASFV-specific antibodies were first detected on the seventh day after immunization; (4) Conclusions: This is the first study to complete the replication and virulence functional exploration of the C84L gene of SY18. In this study, C84L gene was preliminarily found not a necessary gene for replication, gene deletion strain SY18ΔC84L has similar growth characteristics to SY18 in porcine primary alveolar macrophages. The C84L gene affects the virulence of the SY18 strain.

Identification of a novel B-cell epitope of the African swine fever virus p34 protein and development of an indirect ELISA for the detection of serum antibodies

African swine fever (ASF) is a viral disease caused by the African swine fever virus that can be highly transmitted and lethal in domestic pigs. In the absence of a vaccine, effective diagnosis is critical for minimizing the virus's spread. In recent years, with the decline of African swine fever virus (ASFV) virulence, antibody detection has become an important means of detection. ASFV nucleocapsid protein p34 is a mature hydrolytic product of pp220, which is highly conserved and has a high content in the structural protein of the virus. Prokaryotic cells were chosen to generate highly active and high-yield p34 protein, which was then used as an antigen for producing mouse monoclonal antibodies. The B-cell epitope 202QKELDKLQT210, which was highly conserved and found on the surface of the p34 protein, was first identified by an anti-p34 monoclonal antibody utilizing the peptide scanning technique and visualized in helix. This supported the viability of p34 protein detection even further. In addition, we established an indirect ELISA assay based on p34 to detect ASFV antibodies. The coincidence rate of this method with commercially available kits was shown to be 97.83%. Sensitivity analysis revealed that it could be detected in serum dilution as low as 1:6400, and there was no cross-reaction with other prevalent porcine epidemic diseases classical swine fever virus (CSFV), foot-and-mouth disease virus (FMDV), porcine reproductive and respiratory syndrome virus (PRRSV), and porcine circovirus 2 (PCV2). In summary, the established ELISA method and anti-P34 monoclonal antibody have demonstrated that the p34 protein has a promising application prospect for the detection of African swine fever antibodies.

Architecture and Assembly of Structurally Complex Viruses

Viral particles consist essentially of a proteinaceous capsid that protects the genome and is also involved in many functions during the virus life cycle. In structurally simple viruses, the capsid consists of a number of copies of the same, or a few different proteins organized into a symmetric oligomer. Structurally complex viruses present a larger variety of components in their capsids than simple viruses. They may contain accessory proteins with specific architectural or functional roles, or incorporate non-proteic elements such as lipids. They present a range of geometrical variability, from slight deviations from the icosahedral symmetry to complete asymmetry or even pleomorphism. Putting together the many different elements in the virion requires an extra effort to achieve correct assembly, and thus complex viruses require sophisticated mechanisms to regulate morphogenesis. This chapter provides a general view of the structure and assembly of complex viruses.

Identification of the p34 Protein of African Swine Fever Virus as a Novel Viral Antigen with Protection Potential

African swine fever (ASF) is a highly contagious disease caused by African swine fever virus (ASFV), affecting domestic and wild boars. The polyprotein pp220 of ASFV is responsible for producing the major structural proteins p150, p37, p14, p34, and p5 via proteolytic processing. The p34 protein is the main component of the ASFV core shell. However, the immunologic properties of the p34 protein in vitro and in vivo remain unclear. The results showed that the recombinant p34 protein expressed in prokaryotes and eukaryotes could react with convalescent swine sera to ASFV, suggesting that p34 is an immunogenic protein. Significantly, anti-p34 antibodies were found to inhibit the replication of ASFV in target cells. Furthermore, rabbits immunized with the recombinant C-strain of classical swine fever virus containing p34 produced both anti-p34 humoral and cellular immune responses. In addition, the p34 protein could induce a cell-mediated immune response, and a T-cell epitope on the p34 protein was identified using immunoinformatics and enzyme-linked immunospot (ELIspot) assay. Our study demonstrates that the p34 protein is a novel antigen of ASFV with protective potential.

Comparative Analysis of Swine Antibody Responses following Vaccination with Live-Attenuated and Killed African Swine Fever Virus Vaccines

African swine fever virus (ASFV) is circulating in many swine-producing countries, causing significant economic losses. It is observed that pigs experimentally vaccinated with a live-attenuated virus (LAV) but not a killed virus (KV) vaccine develop solid homologous protective immunity. The objective of this study was to comparatively analyze antibody profiles between pigs vaccinated with an LAV vaccine and those vaccinated with a KV vaccine to identify potential markers of vaccine-induced protection. Thirty ASFV seronegative pigs were divided into three groups: Group 1 received a single dose of an experimental LAV, Group 2 received two doses of an experimental KV vaccine, and Group 3 was kept as a non-vaccinated (NV) control. At 42 days post-vaccination, all pigs were challenged with the parental virulent ASFV strain and monitored for 21 days. All pigs vaccinated with the LAV vaccine survived the challenge. In contrast, eight pigs from the KV group and seven pigs from the NV group died within 14 days post-challenge. Serum samples collected on 41 days post-vaccination were analyzed for their reactivity against a panel of 29 viral structural proteins. The sera of pigs from the LAV group exhibited a strong antibody reactivity against various viral structural proteins, while the sera of pigs in the KV group only displayed weak antibody reactivity against the inner envelope (p32, p54, p12). There was a negative correlation between the intensity of antibody reactivity against five ASFV antigens, namely p12, p14, p15, p32, and pD205R, and the viral DNA titers in the blood of animals after the challenge infection. Thus, antibody reactivities against these five antigens warrant further evaluation as potential indicators of vaccine-induced protection.

[Adaptation of african swine fever virus (Asfarviridae: Asfivirus)to growth in the continuous culture PPK-66b cells by the method of accelerated passaging]

INTRODUCTION

African swine fever virus (ASF) is a large, enveloped virus with an icosahedral capsid morphology and a double-stranded DNA genome ranging in size from 170 to 190 kb. The replication cycle proceeds in two phases, the early phase lasting 4-6 hours and the late 8-20 hours after infection. The adaptation of the ASF virus to growth in continuous cell lines makes efficient and reliable genetic analysis and more accurate interpretation of its results.

OBJECTIVE

Adaptation of a new isolate of the ASF virus to growth in a continuous cell line by the method of accelerated passages and preliminary genetic analysis of the resulting strain.

MATERIALS AND METHODS

For virus isolation and passaging of the ASF virus, a porcine leukocyte cell culture (PL) and continuous cell cultures of porcine origin (ST, PK, PPK-66b) were used with Eagle MEM and HLA essential media with 10% porcine or fetal serum.

RESULTS

The article presents data on the isolation and analysis of the changes in the reproductive properties of a new African swine fever (ASF) virus isolate in the process of adaptation to growth in a continuous piglet kidney cell culture clone b (PPK-66b). The current state of the problem of cultivation of the ASF virus, the features of its reproduction, and the basis of the genetic differentiation of its isolates are described in detail. Understanding the uniqueness of the nature of the ASF virus determined the approaches to the processes of its cultivation and adaptation. In this regard, the results of studies of cultural properties, and analysis of the nucleotide sequence of 6 genes of the new isolate, as well as phylogenetic analysis of these genes with already known strains and isolates of the ASF virus are presented.

CONCLUSION

A new strain obtained in the process of cell adaptation of ASVF/Znaury/PPK-23 ASF virus by the accelerated passaging method reaches a high level of reproduction in 72 hours with an accumulation titer of 7.07 lg HAdE50/cm3. Primary genetic analysis allowed to establish the main phylogenetic relationships of the newly isolated strain with previously known variants of the current ASF panzootic.

Computational analysis of immunogenic epitopes in the p30 and p54 proteins of African swine fever virus

African swine fever (ASF) is a highly infectious viral disease of pigs, which causes acute fatal haemorrhage and is a severe concern to the global pork industry. The present study followed computational approaches to identify B- and T-cell epitopes for the p30 and p54 proteins of the African swine fever virus (ASFV) by interacting with the swine leukocyte antigen (SLA) alleles. The amino acid sequences of p30 and p54 were analysed for variability and relative solvent accessibility, and their three-dimensional structures were predicted and validated. Molecular dynamics simulation was performed to study the structural and dynamic properties of the protein. Six and five linear B-cell epitopes have been predicted for p30 and p54, respectively. Four and three discontinuous B-cell epitopes have been predicted for p30 and p54, respectively. Further, the top five T-cell epitopes for SLA-1, 2, and 3 have been listed for both proteins. These results can help us to understand the immunodominant regions in the p30 and p54 proteins of ASFV and potentially assist in designing peptide-based diagnostics and vaccines. Also, the identified T-cell epitopes may be considered for peptide-based vaccine design against ASFV.Communicated by Ramaswamy H. Sarma.

Genetic analysis of African swine fever viruses based on E183L (p54) gene, circulating in South Sumatra and Lampung province, Indonesia

Background and Aim

African swine fever (ASF) is a disease that emerged in Indonesia in 2019 in the North Sumatra province and spread rapidly to other areas, such as South Sumatra and Lampung, in 2020. This study aimed to identify the phylogenetics of the ASF virus (ASFV) in the provinces of South Sumatra and Lampung.

Materials and Methods

Nine ASFV isolates collected from the Disease Investigation Center in Lampung were used in this study. The isolates were from ASF cases in South Sumatra and Lampung in 2020-2022. The isolates were sequenced and compared with other ASFV isolates to establish the virus genotype. Sequencing was performed using the complete E183L gene target encoding the p54 protein.

Results

This study showed that ASFV from South Sumatera and Lampung Province belongs to genotype II.

Conclusion

Based on the analysis of the E183L gene, all nine ASFV isolates that originated from South Sumatra and Lampung were identical to other genotype II ASFV isolates from Georgia, China, Vietnam, and Timor Leste.

Establishment of a Dual-Antigen Indirect ELISA Based on p30 and pB602L to Detect Antibodies against African Swine Fever Virus

African swine fever (ASF) is an acute, virulent, and highly fatal infectious disease caused by the African swine fever virus (ASFV). There is no effective vaccine or diagnostic method to prevent and control this disease currently, which highlights the significance of ASF early detection. In this study, we chose an early antigen and a late-expressed antigen to co-detect the target antibody, which not only helps in early detection but also improves accuracy and sensitivity. CP204L and B602L were successfully expressed as soluble proteins in an Escherichia coli vector system. By optimizing various conditions, a dual-antigen indirect ELISA for ASFV antibodies was established. The assay was non-cross-reactive with antibodies against the porcine reproductive and respiratory syndrome virus, classical swine fever virus, porcine circovirus type 2, and pseudorabies virus. The maximum serum dilution for detection of ASFV-positive sera was 1:1600. The intra-batch reproducibility coefficient of variation was <5% and the inter-batch reproducibility coefficient of variation was <10%. Compared with commercial kits, the dual-antigen indirect ELISA had good detection performance. In conclusion, we established a detection method with low cost, streamlined production process, and fewer instruments. It provides a new method for the serological diagnosis of ASF.

The non-classical major histocompatibility complex II protein SLA-DM is crucial for African swine fever virus replication

African swine fever virus (ASFV) is a lethal animal pathogen that enters its host cells through endocytosis. So far, host factors specifically required for ASFV replication have been barely identified. In this study a genome-wide CRISPR/Cas9 knockout screen in porcine cells indicated that the genes RFXANK, RFXAP, SLA-DMA, SLA-DMB, and CIITA are important for productive ASFV infection. The proteins encoded by these genes belong to the major histocompatibility complex II (MHC II), or swine leucocyte antigen complex II (SLA II). RFXAP and CIITA are MHC II-specific transcription factors, whereas SLA-DMA/B are subunits of the non-classical MHC II molecule SLA-DM. Targeted knockout of either of these genes led to severe replication defects of different ASFV isolates, reflected by substantially reduced plating efficiency, cell-to-cell spread, progeny virus titers and viral DNA replication. Transgene-based reconstitution of SLA-DMA/B fully restored the replication capacity demonstrating that SLA-DM, which resides in late endosomes, plays a crucial role during early steps of ASFV infection.

SY18ΔL60L: a new recombinant live attenuated African swine fever virus with protection against homologous challenge

Introduction

African swine fever (ASF) is an acute and highly contagious disease and its pathogen, the African swine fever virus (ASFV), threatens the global pig industry. At present, management of ASF epidemic mainly relies on biological prevention and control methods. Moreover, due to the large genome of ASFV, only half of its genes have been characterized in terms of function.

Methods

Here, we evaluated a previously uncharacterized viral gene, L60L. To assess the function of this gene, we constructed a deletion strain (SY18ΔL60L) by knocking out the L60L gene of the SY18 strain. To evaluate the growth characteristics and safety of the SY18ΔL60L, experiments were conducted on primary macrophages and pigs, respectively.

Results

The results revealed that the growth trend of the recombinant strain was slower than that of the parent strain in vitro. Additionally, 3/5 (60%) pigs intramuscularly immunized with a 105 50% tissue culture infectious dose (TCID50) of SY18ΔL60L survived the 21-day observation period. The surviving pigs were able to protect against the homologous lethal strain SY18 and survive. Importantly, there were no obvious clinical symptoms or viremia.

Discussion

These results suggest that L60L could serve as a virulence- and replication-related gene. Moreover, the SY18ΔL60L strain represents a new recombinant live-attenuated ASFV that can be employed in the development of additional candidate vaccine strains and in the elucidation of the mechanisms associated with ASF infection.

Functional Landscape of African Swine Fever Virus-Host and Virus-Virus Protein Interactions

Viral replication fully relies on the host cell machinery, and physical interactions between viral and host proteins mediate key steps of the viral life cycle. Therefore, identifying virus-host protein-protein interactions (PPIs) provides insights into the molecular mechanisms governing virus infection and is crucial for designing novel antiviral strategies. In the case of the African swine fever virus (ASFV), a large DNA virus that causes a deadly panzootic disease in pigs, the limited understanding of host and viral targets hinders the development of effective vaccines and treatments. This review summarizes the current knowledge of virus-host and virus-virus PPIs by collecting and analyzing studies of individual viral proteins. We have compiled a dataset of experimentally determined host and virus protein targets, the molecular mechanisms involved, and the biological functions of the identified virus-host and virus-virus protein interactions during infection. Ultimately, this work provides a comprehensive and systematic overview of ASFV interactome, identifies knowledge gaps, and proposes future research directions.

African Swine Fever Virus Gene B117L Encodes a Small Protein Endowed with Low-pH-Dependent Membrane Permeabilizing Activity

African swine fever virus (ASFV) is causing a devastating pandemic in domestic and wild swine in Central Europe to East Asia, resulting in economic losses for the swine industry. The virus contains a large double-stranded DNA genome that contains more than 150 genes, most with no experimentally characterized function. In this study, we evaluate the potential function of the product of ASFV gene B117L, a 115-amino-acid integral membrane protein transcribed at late times during the virus replication cycle and showing no homology to any previously published protein. Hydrophobicity distribution along B117L confirmed the presence of a single transmembrane helix, which, in combination with flanking amphipathic sequences, composes a potential membrane-associated C-terminal domain of ca. 50 amino acids. Ectopic transient cell expression of the B117L gene as a green fluorescent protein (GFP) fusion protein revealed the colocalization with markers of the endoplasmic reticulum (ER). Intracellular localization of various B117L constructs also displayed a pattern for the formation of organized smooth ER (OSER) structures compatible with the presence of a single transmembrane helix with a cytoplasmic carboxy terminus. Using partially overlapping peptides, we further demonstrated that the B117L transmembrane helix has the capacity to establish spores and ion channels in membranes at low pH. Furthermore, our evolutionary analysis showed the high conservation of the transmembrane domain during the evolution of the B117L gene, indicating that the integrity of this domain is preserved by the action of the purifying selection. Collectively our data support a viroporin-like assistant role for the B117L gene-encoded product in ASFV entry. IMPORTANCE ASFV is responsible for an extensively distributed pandemic causing important economic losses in the pork industry in Eurasia. The development of countermeasures is partially limited by the insufficient knowledge regarding the function of the majority of the more than 150 genes present on the virus genome. Here, we provide data regarding the functional experimental evaluation of a previously uncharacterized ASFV gene, B117L. Our data suggest that the B117L gene encodes a small membrane protein that assists in the permeabilization of the ER-derived envelope during ASFV infection.

Structural Insights into the Assembly of the African Swine Fever Virus Inner Capsid

African swine fever virus (ASFV), the cause of a highly contagious hemorrhagic and fatal disease of domestic pigs, has a complex multilayer structure. The inner capsid of ASFV located underneath the inner membrane enwraps the genome-containing nucleoid and is likely the assembly of proteolytic products from the virally encoded polyproteins pp220 and pp62. Here, we report the crystal structure of ASFV p150△NC, a major middle fragment of the pp220 proteolytic product p150. The structure of ASFV p150△NC contains mainly helices and has a triangular plate-like shape. The triangular plate is approximately 38 Å in thickness, and the edge of the triangular plate is approximately 90 Å long. The structure of ASFV p150△NC is not homologous to any of the known viral capsid proteins. Further analysis of the cryo-electron microscopy maps of the ASFV and the homologous faustovirus inner capsids revealed that p150 or the p150-like protein of faustovirus assembles to form screwed propeller-shaped hexametric and pentametric capsomeres of the icosahedral inner capsids. Complexes of the C terminus of p150 and other proteolytic products of pp220 likely mediate interactions between the capsomeres. Together, these findings provide new insights into the assembling of ASFV inner capsid and provide a reference for understanding the assembly of the inner capsids of nucleocytoplasmic large DNA viruses (NCLDV). IMPORTANCE African swine fever virus has caused catastrophic destruction to the pork industry worldwide since it was first discovered in Kenya in 1921. The architecture of ASFV is complicated, with two protein shells and two membrane envelopes. Currently, mechanisms involved in the assembly of the ASFV inner core shell are less understood. The structural studies of the ASFV inner capsid protein p150 performed in this research enable the building of a partial model of the icosahedral ASFV inner capsid, which provides a structural basis for understanding the structure and assembly of this complex virion. Furthermore, the structure of ASFV p150△NC represents a new type of fold for viral capsid assembly, which could be a common fold for the inner capsid assembly of nucleocytoplasmic large DNA viruses (NCLDV) and would facilitate the development of vaccine and antivirus drugs against these complex viruses.

New perspective on African swine fever: a bibliometrics study and visualization analysis

Introduction

African swine fever (ASF) is a contagious viral disease that can have devastating effects on domestic pigs and wild boars. Over the past decade, there has been a new wave of this ancient disease spreading around the world, prompting many scholars to dedicate themselves to researching this disease. This research aims to use bibliometric methods to organize, analyze and summarize the scientific publications on ASF that have been amassed in the past two decades.

Methods

This paper used VOSviewer, CiteSpace, and a bibliometric online analysis platform to conduct performance analysis and visualization studies on 1,885 academic papers about ASF in the Web of Science from January 2003 to December 2022.

Results

The amount of literature published on ASF has increased exponentially in recent years, and the development trend of related research is good. A group of representative scholars have appeared in this research field, and some cooperative networks have been formed. Transboundary and Emerging Diseases is the journal with the most publications in this field, while Virus Research is the journal with the most citation per article. High-productivity countries are led by China in terms of the number of articles published followed by the United States and Spain. In regard to the average number of citations, the scholars in the UK are in the lead. The institution with the most articles was the Chinese Academy of Agricultural Sciences. The analysis of high-frequency keywords showed that the pathogens and epidemiology of ASF were the research hotspots in this field, and the research content was closely related to molecular biology and immunology. The burst keywords "transmission", "identification", "virulence", "replication", and "gene" reflects the research frontier. In addition, by collating and analyzing highly cited journals and highly co-cited references, we explored the knowledge structure and theoretical basis of this field.

Discussion

This is the first bibliometric analysis report on ASF research, which highlights the key characteristics of ASF research and presents the research status and evolution trend in this field from a new perspective. It provides a valuable reference for further research.

Identification of monoclonal antibody targeting epitope on p72 trimeric spike of African swine fever virus

African swine fever virus (ASFV) is highly contagious and can cause lethal disease in pigs. ASFV p72 protein is a major capsid protein that presents as trimer in the virion. Epitopes on the surface of p72 trimer are considered as protective antigens. In this study, recombinant p72 protein and p72-baculovirus were constructed and obtained. Three monoclonal antibodies (mAbs) specific to ASFV p72 protein, designated as 1A3, 2B5 and 4A5, were generated. Among them, 4A5 showed strong reactivity with ASFV infected cells. Subsequently, the epitope recognized by 4A5 was mapped and identified using a series of overlapping peptides generated from p72 protein. IFA and western blot analyses showed that 4A5 recognized the linear epitope of p72 monomer located between amino acids 245-285 and recognized the conformational epitope located at the surface and top of the p72 trimer. These findings will enrich our knowledge regarding the epitope on p72 protein and provide valuable information for further characterization of the antigenicity and molecular functions of p72 protein.

PI3K-Akt pathway-independent PIK3AP1 identified as a replication inhibitor of the African swine fever virus based on iTRAQ proteomic analysis

African swine fever (ASF) is a severe infectious disease that has a high global prevalence. The fatality rate of pigs infected with ASF virus (ASFV) is close to 100%; in the absence of a safe and reliable commercial vaccine, this poses a threat to the global pig industry and public health. To better understand the interaction of ASFV with its host, isobaric tags for relative and absolute quantitation combined with liquid chromatography-mass spectrometry was used to conduct quantitative proteomic analysis of bone marrow-derived macrophage cells infected with ASFV. Overall, 4579 proteins were identified; 286 of these were significantly upregulated and 69 were significantly downregulated after ASFV infection. Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, and protein-protein interaction network analyses were used to obtain insights into the dynamics and complexity of the ASFV-host interaction. In addition, immunoblotting revealed that the expression of PIK3AP1, RNF114, and FABP5 was upregulated and that of TRAM1 was downregulated after ASFV infection. Overexpression of PIK3AP1 and RNF114 significantly inhibited ASFV replication in vitro, but the suppressive effect of PIK3AP1 on ASFV replication was independent of the PI3K-Akt pathway. Further studies confirmed that ASFV MGF360-9L interacts with PIK3AP1 to reduce its protein expression level. Moreover, LY294002, an inhibitor of the PI3K-Akt pathway, inhibited ASFV replication, indicating the importance of the PI3K-Akt pathway in ASFV infection. This study identified the network of interactions between ASFV and host cells and provides a reference for the development of anti-ASFV strategies and for studying the potential mechanisms and pathogenesis of ASFV infection.

Inactivation Performance of Pseudorabies Virus as African Swine Fever Virus Surrogate by Four Commercialized Disinfectants

This study was based on similar physicochemical characteristics of pseudorabies virus (PRV) and African swine fever virus (ASFV). A cellular model for evaluation of disinfectants was established with PRV as an alternative marker strain. In the present study, we evaluated the disinfection performance of commonly used commercialized disinfectants on PRV to provide a reference for the selection of good ASFV disinfectants. In addition, the disinfection (anti-virus) performances for four disinfectants were investigated based on the minimum effective concentration, onset time, action time, and operating temperature. Our results demonstrated that glutaraldehyde decamethylammonium bromide solution, peracetic acid solution, sodium dichloroisocyanurate, and povidone-iodine solution effectively inactivated PRV at concentrations 0.1, 0.5, 0.5, and 2.5 g/L on different time points 30, 5, 10, and 10 min, respectively. Specifically, peracetic acid exhibits optimized overall performance. Glutaraldehyde decamethylammonium bromide is cost effective but requires a long action time and the disinfectant activity is severely affected by low temperatures. Furthermore, povidone-iodine rapidly inactivates the virus and is not affected by environmental temperature, but its application is limited by a poor dilution ratio such as for local disinfection of the skin. This study provides a reference for the selection of disinfectants for ASFV.

Novel Epitopes Mapping of African Swine Fever Virus CP312R Protein Using Monoclonal Antibodies

African Swine Fever (ASF) is a highly contagious and lethal pig disease and poses a huge threat to the pig industry worldwide. ASF virus (ASFV) encodes more than 150 different proteins, but the biological properties of most viral proteins are still unknown. ASFV CP312R protein has been proven to be one of the most immunogenic proteins during ASFV infection in pigs; however, its specific epitopes have yet to be identified. In this study, we verified the immunogenicity of CP312R protein in the sera from attenuated ASFV-inoculated pigs. We generated seven anti-ASFV CP312R mouse monoclonal antibodies (mAbs) from mice immunized with recombinant CP312R protein (rCP312R). All seven mAbs are the IgG2b-Kappa isotype and specifically interacted with the CP312R protein expressed in various cells that were infected by ASFVs or transfected with plasmid CP312R. The epitope mapping was performed by using these characterized mAbs and the peptide scanning (Pepscan) method followed by Western blot. As a result, two antigenic determinant regions were identified: two of the seven mAbs recognized the ¹²²KNEQGEEIYP¹³¹ amino acids, and the remaining five mAbs recognized the ⁷⁸DEEVIRMNAE⁸⁷ amino acids of the CP312R protein. These antigenic determinants of CP312R are conserved in different ASFV strains of seven genotypes. By using the characterized mAb, confocal microscopy observation revealed that the CP312R was mainly localized in the cytoplasm and, to some extent, in nuclei and on the nuclear membrane of infected host cells. In summary, our results benefit our understanding on the antigenic regions of ASFV CP312R and help to develop better serological diagnosis of ASF and vaccine research.

African swine fever virus transmembrane protein pEP84R guides core assembly

African swine fever virus (ASFV) causes a devastating hemorrhagic disease with worldwide circulation and no widely available therapeutic prevention. The infectious particle has a multilayered architecture that is articulated upon an endoplasmic reticulum (ER)-derived inner envelope. This membrane acts as docking platform for the assembly of the outer icosahedral capsid and the underlying core shell, a bridging layer required for the formation of the central genome-containing nucleoid. While the details of outer capsid assembly are relatively well understood, those of core formation remain unclear. Here we report the functional characterization of pEP84R, a transmembrane polypeptide embedded in the inner envelope that surrounds the viral core. Using an ASFV recombinant inducibly expressing the EP84R gene, we show that absence of pEP84R results in the formation of non-infectious core-less icosahedral particles displaying a significant DNA-packaging defect. Concomitantly, aberrant core shell-like structures formed by co-assembly of viral polyproteins pp220 and pp62 are mistargeted to non-ER membranes, as also occurs when these are co-expressed in the absence of other viral proteins. Interestingly, co-expression of both polyproteins with pEP84R led to the formation of ER-targeted core shell-like assemblies and co-immunoprecipitation assays showed that pEP84R binds to the N-terminal region of pp220. Altogether, these results indicate that pEP84R plays a crucial role in core assembly by targeting the core shell polyproteins to the inner viral envelope, which enables subsequent genome packaging and nucleoid formation. These findings unveil a key regulatory mechanism for ASFV morphogenesis and identify a relevant novel target for the development of therapeutic tools against this re-emerging threat.